Parents who welcomed their first child on Wednesday were surprised to learn the original name they had picked was actually in the top four most popular girls’ names.

Rachel and Steven McMaster decided together they wanted to name their daughter Isla Ashlee.

“We thought it was a unique name,” Mr McMaster laughed.

“When we saw her, we both knew that we wanted to call her Isla.”

The parents were surprised, but happy to learn their choice wasn’t as original as they thought.

“I suppose it’s the trending thing so it’s nice to know that other people thought it was a beautiful name.”

These names will soon dominate NSW primary school roll-calls

Boys called Oliver are going to utterly dominate NSW primary school roll-calls in coming years – if they aren't already.

The name topped the state's Register of Births, Deaths and Marriages list of 100 most popular baby names (for boys) for the fourth year in a row last year.

The second most popular boys' name, William, has sat in second place for each of those four years, having been toppled from the number one spot it held in 2013.

For girls, Charlotte bumped out the 2016 winner – Olivia – for first place in 2017. The two girls' names have been neck-and-neck for first and second place for the past three years.

While Australia's obsession with Oliver and Olivia cannot be explained, the enduring popularity of Charlotte and William is likely helped by their namesakes in the Royal Family, according to BDM Registrar Amanda Ianna.

"We are seeing little change in the most popular names, but there definitely seems to be a Royal flavour in the air," she told Fairfax media.

With the birth of Princess Charlotte's new baby brother Louis last month, it's expected his name will shoot up the charts for this year. Last year Louis came in at 70th, while George, their older brother's name, was 28th.

"Mums and Dads are also wild about Harry with his name jumping from 27 to 21. While his real name, Henry, was the biggest mover on the list finishing seventh last year up from 18th in 2016," Ms Ianna said.

Along with Henry, other newcomers in the top 10 were Ella and Zoe for girls, replacing Emily and Ruby.

Meanwhile, Elizabeth is still making the grade at number 46, but Catherine and Megan (or Meghan) haven’t been seen in the top 100 since the early 2000s.

"Whether it’s significant to your heritage, trendy or unique, it’s important to choose wisely as your child will carry their name for life," Ms Ianna said.